Biological molecules 2.1.2 Carbohydrates Flashcards
Monosaccarides and diasaccarides
A monosaccaride is a single sugar unit e.g. glucose, fructose and ribose. When 2 monosaccarides link together they form a diasaccaride e.g. lactose and sucrose. When two or more monosaccarides are linked it forms a polysaccaride e.g. glycogen, cellulose and starch.
Monosaccarides
Monomer of carbohydrates, they are sugars, have the general formula (CH2O)n where n is either 3 5 or 6. Contain the functional group OH and dissolve in water
When n = 3
- The formula would be C3 H6 O3
- The sugar is called triose
- Triose phosphate = sugar involved in respiration and photosynthesis.
When n=5
- The formula would be C5 H10 O5
- Sugar is called pentose
- e.g. ribose in RNA, ATP and deoxyribose in DNA
The structure of ribose
*Look at powerpoint
When n=6
- The formula would be C6 H12 O6
- Sugar is called hexose
- e.g. glucose transports sugar in animals and the main respiratory substrate
- Fructose, found in plant transport sugar
- Galactose found in milk sugar
- All hexoses are structural isomers (same chemical formula but different molecular structure)
Structure of alpha glucose
- look on power point
Structure of beta glucose
*look on power point
Glucose molecules
They are polar and soluble in water due to the hydrogen bonds that form between the hydroxl groups and the water molecules. The solubility id important because it means glucose is dissolved into the cytosol of the cell.
Difference between alpha and beta glucose
- For alpha the -OH on c1 is below the plane of the ring and on the same side as the -OH on c4
- For beta -OH on c1 is above the ring and the opposite side to -OH on c4
Ribose
Number of carbons = 5
Number of carbons in ring = 4
Type of ring = 5 membered
Oxygen atom present in ring? = yes
Chemical formula = C5 H10 O5
Glucose
Number of carbons = 6
Number of carbons in ring = 5
Type of ring = 6 membered
Oxygen atom present in ring? = yes
Chemical formula = C6 H12 O6
Fructose
Number of carbons = 6
Number of carbons in ring = 4
Type of ring = 5 membered
Oxygen atom present in ring? = yes
Chemical formula = C6 H12 O6
Diasaccarides
- 2 monosaccarides joined together by a condensation reaction
General formula = (C6 H12 O6)2 - H2O= C12 H22 O11
Maltose
- Present in germinating seeds
- Function = source of energy for germination
- Structure = look on powerpoint
- The bond formed between 2 monosaccarides is a glycosidic bond
- Disaccarides can be broken by a hydrolysis reaction
Sucrose
- Transport sugar in the phloem
- Composed of alpha glucose and fructose
- a non reducing sugar
- see on pp for structure
Lactose
- Milk sugar
- Composed of glucose and beta galactose
- Joined together by a a beta 1,4 glycosidic bond (the glucose and galactose are flipped with respect to eachother)
Polysaccarides
- Polymer of carbohydrates
- Long chain of carbohydrate molecules made up of condensed monosaccarides
-There are 3 common types which are all polymers of glucose (C6 H12 O6)
General formula of polysaccarides
(C6 H10 O5)x + (H2O)
where x = number of monomers in the chain.
Starch
- Function molecule in plants
- Source of glucose/ energy for respiration
- Insoluble so does not affect water potential of the cell
- Found in chloroplasts, amyloplasts
- Storage organs: tubers(for asexual reproduction), seeds (grain, following sexual reproduction).
Amylose (structure)
- 20% of starch
- Monomer = alpha glucose
- Bonds = alpha 1,4 glycosidic bonds
- Structure = Helical molecule, helix held together by intramolecular H molecules.
- Mr = 50000
- About 300 glucose residues in a molecule of amylose
- Look at structure on pp
Amylopectin
- 80% of starch
- monomer = alpha glucose
- Mr = 500000
- About 3000 glucose residules in a molecule of amylopectin
- Bonds = 1,4 and 1,6 glycosidic bonds
- Structure = branched